Two consumer groups urged U.S. regulators on Monday to block Google from acquiring mobile advertising provider AdMob, citing potential harm the deal could cause to users, advertisers and application developers.

Google's plan to acquire AdMob for US$750 million, announced last month, "would substantially lessen competition in the increasingly important mobile advertising market," said the letter, signed by representatives of the groups Consumer Watchdog and Center for Digital Democracy. It was addressed to the Federal Trade Commission, the regulatory body that Google last week said had asked the company for more information about the deal.

Google did not immediately reply to a request for comment, but the company has said it does not see any regulatory issues with the purchase. "The rapidly growing mobile advertising space is highly competitive with more than a dozen mobile ad networks," Paul Feng, a Google product manager, said in an official blog post last week.

The consumer groups argued in the letter that the combined body of information about consumer behavior gathered by Google and AdMob would threaten user privacy. It also argued that the buyout would reduce competition by bolstering Google's dominance in the advertising industry and could hurt mobile application developers, who would have fewer choices when seeking a revenue-sharing partner for ads in their apps.